Abelson murine leukemia virus is a rapidly transforming retrovirus that induces pre-B cell lymphoma and transforms pre-B lymphocytes and NIH 3T3 fibroblasts in vitro. The v-Abl protein tyrosine kinase mediates these responses and transmits signals that stimulate growth and suppress apoptosis and differentiation. All of these signals must be appropriately integrated for transformation to occur. A combination of genetic approaches will be used to determine how v-AbI accomplishes this. We will focus on three areas. A combination of genetic and biochemical approaches will be used to study the role of the v-Abl SH2 domain in mediating signals from v-AbI to downstream mediators. Two mutants will be used, a conditional mutant that is compromised for transformation at 39 degrees celcius, and a mutant that encodes a chimeric v-Abl/v-Src protein that fails to transform cells. In a second aim, we will examine the mechanism by which the COOH terminus of v-Abl affects lymphoid cell transformation. The role of the Ras pathway in this response will be investigated using a genetic complementation strategy and sequences at the extreme COOH terminal end of the protein will be identified using a series of deletion and truncation mutants. The mechanism by which these sequences influence the transformation process will be studied by identifying the cellular targets that are affected by these sequences. In the last aim, we will use a unique weakly oncogenic AbMLV mutant that generates highly oncogenic variants in vivo to understand the selective pressures that affect c-onc gene evolution. The dynamics and complexity of the viral population during the selection process and the role of target cell growth stimulation will be tested to uncover features that control this process. These events are likely to mimic those that occur during the v-onc gene capture and should advance our understanding of the way in which v-onc gene containing viruses arise and induce tumors.